This invention relates to drilling of horizontal boreholes through subterranean formations, and more particularly to drilling of horizontal boreholes through formations traversed by a cased well.
There is a renewed interest in horizontal drainholes in the petroleum industry. Used in the proper reservoirs, horizontal drainholes can provide an economic alternative to vertical wells with or without stimulation. Since the horizontal well concept was introduced in the 1930's, drilling, completion, and production technology have significantly improved. The applications for drainhole technology have generally fallen into five categories. The first is in high permeability formations. A second application is for reservoirs which have heterogeneous permeability distribution, such as naturally fractured formations. The third is for increased production rates where water or gas coning is a problem. A fourth is to improve the areal sweep efficiency of secondary and tertiary recovery projects. The final application is in thermally enhanced recovery of heavy oil, such as steam floods and fire floods. Horizontal wells can provide higher production rates, improved recoveries, better areal sweep, and can reduce the need for additional wells.